Manufacture of chlorine



Feb. 11, 1930. F. s. Low

MANUFACTURE oF CHLORINE Filed Oct. 25, 1928 aff/2v (ktm ne q PatentedFeb. '11, 1930 UNITED sTATEs PATENT oFFIcE FRANK S. LOW, OF NIAGARA.FALLS, NEW-YORK, ASSIGNOR TO WESTVACO CHLORINE PRODUCTS, INC., OF NEWYORK, N. Y., A. CORPORATION F VIRGINIA MANUFACTURE 0F CHLORINEApplication filed October 25, 1928. Serial No. 315,007.

This invention relates to the manufactureof chlorine; and it comprises amethod of producing chlorine by electrolysis of a solution ofhydrochloric acid (HC1) wherein a body oir' such solution is establishedand maintained between electrodes of opposed polarity in a suitable celland the acidity replenished as it tends to disappear by addition of HC1gas :to said body at a point below the electrode m level; and it alsocomprises certain assemblages of apparatus elements useful in the saidmethod; all as more fully hereinafter set forth and as claimed.

hlorine is commercially made by electrolysis of solutions of salt;caustic soda in the corresponding amount being also produced. To securegood utilization of the salt and recover caustic soda from the cellliquor, ex-

` tensive auxiliary apparatus is required and.

2o the process is one best operated on a large scale. There is, however,a demand' for a method of producing chlorine which can be economicallyoperated on a smaller scale and which is not coupledwith the productionof a5 caustic soda. llt is the object of the present invention toprovide such a method.

ln the present invention, chlorine is made by electrolysis of asolution'of HC1` (hydrochloric acid) replenished by .additions of sogaseous HCl. Formation of chlorine from HC1 requires less energy thanits formation from NaCl. The electrolytic operation is tar simpler,since only gases (Cl2 and H2) are formed and there is no production ofsoluble byproducts in the cell liquor. The same body of electrolyte mayserve indeiinitely without removal from the cell, since the input of HClgas is proportioned to the chlorine output, and but-little attention isrequired. The op- 49 eration of a cell becomes almost automatic.

The HC1 gas used in replenishment may be made in an of the usual ways,as by the action of sul uric acid on salt.

In the accompanying illustration, I have shown, more or lessdiagrammatically, .an electrolytic cell within the present invention anduseful in performance of my process. The view is in central verticalsection.

As shown, element 1 is a casing of any suitable insulating andacid-proof material. It

is shown as carrying a cap 2 having Wing 3 dependingbelow the normalliquid level of v the electrolyte, forming an annular chlorine chamber.As shown, from the wing depends an annular screen member 4- of looselywoven asbestos or other pervious acid resistant material. lt extends toa point just above the bottom. Through the cover for the anodecompartment pass chlorine outlet pipe 5 and current lead 6, supplyingcurrent to anode 7.. As shown, the anode is annular. It may be composedof graphite or other usual material. Supported by annular cap 2 isanother cover element 8 for the axial cathode compartment. Through itpasses current lead 9 taking curn rent to a cathode immersed within thebody of electrolyte. As shown, the cathode is drumV-shaped, head 10closing the axial compartment formed by .annular member 11 whichconstitutes the cathode. Near the top, the wall 11 is provided with lowpassages 13. YThrough thecover 8 passes hydrogen outlet 14. The wholesystem is run hot to reduce resistance and the electrolyte may be at thelboiling temperature, although l find it better to work at a somewhatless temperature. The escaping hydrogen is therefore usually cooled toreturn entrained HCl and water vapor to the system. As shown, thehydrogen passes through a scrubber l5 pro- 80 vided with a water inletl5. The scrubber acts as a reflux condenser to return HC1 and water. Asimilar reflux condenser may be provided for chlorine outlet 5 but isnot really needed, since the chlorine goes through 8 the usual purifyingtrain (not shown). As shown, the casing 1 is provided with an axialdependmg well 16. The upper end of this well is somewhat above thebottom of 1. Near the base of the well is a perforated or foraminousplate V17, acting as a distributor for HC1 gas. Below this distributoris inlet pipe 18 :tor HC1 gas; this pipe being provided with check valve19. Except in starting, this check valve is not necessary, for reasonslater appearing. Liquid communication is established between the bottomof casing 1 and a low point in the well by circulating and equalizmgp1pe 20. This pipe serves to control the normal height of electrolyte inthe cell l and is provided with outlet 21 through which excess of cellliquor may be removed. To aid in circulation, pipe 2O may be cooled bywater jacket 22. R

In normal operation, the axial chamber and well contain a hot strongsolution of HC1; the temperature and strength depending somewhat oncircumstances. A saturated solution, which is 20 er cent or thereabouts,boils at about 110 have the temperature at least 10 lower. Actualebullition is undesirable as carrying gaseous HC1 into the cathode gaschamber. For the same reason, saturated solutions are not so desirableas those of somewhat less concentration.' The less the HClconcentration, the easier it is to keep HCl in aqueous solution; but arather high concentration, depending on the speed of ilow between theelectrode and the current density, must be maintained in the axialchamber to provide for the removal of HCl by electrolysis. If the acidpassing between the electrodes is stripped too far, not only is there anincrease in resistance, but oxygen evolution may tend to occur withformation of perchloric acid. It is generally safe to adjust conditionsso that the return flow of acid in pipe 20 shall be not less than .015per cent HC1 and the axial concentration about 20 per cent. Hydrochloricacid gas entering through 18 passes upward through 17 as bubbles and isabsorbed, for the most part, before it reaches the top of the well 16.Passages 13 prevent the top of the axial chamber becoming gas bound andpermit outward flow of liquid. Imperforate top 10 may be replaced by aspider or open structure supported by 11- and carrying current from lead9; but the imperforate disk 10 shown is generally more advantageous, asitprevents direct access of ascending HC1 bubbles to the hydrogenchamber. The lower` the chamber, the more advantageous is the use ofdisk 10. The absorption of the gas by the strong HCl solution in theaxial chamber is not so rapid as to cause suckin back into pipe 18, sothat check valve 19 rare y functions. In normal operation of the cell,the axial chamber contains strong HC1 solution which passes upward andoutward through vents 13, passing thence downward between the electrodesand back to the axial well via circulating pipe 20. HCl gas coming inthrough inlet 18 is sometimes rather hot, since it usually comesdirectly from the place of product-ion. The gas may be precoole'd wherethis is desirable in any of the ordinary ways and by the ordinaryapparatus. It may carry more or less water vapor. It is convenient tosupply such further water as may be needed in the system through pipe 15supplying the hydrogen scrubber.

In the assemblage of the apparatus shown, any of the usual structuralmaterials resistand it is desirable to' 'of PbCL gives it resistance onshutdown. .Screen @shown servesmainly to prevent mixing of gas bubblesand is not intended to retard ion1c migration. Its use facilitatesplaclng the cathode and anode in close approximation and therebylessening resistance. The screen is advantageous, and particularly intall types of cell, but not necessary.

Resaturation of the electrolyte can be done outside the cell proper, butthe arrangement shown is better. It avoids handling acid solution andthe use of pipe lines.

What I claim is 1. In the manufacture of chlorine, the process whichcomprises electrolyzing a body of aqueous solution of HC1 between a pairof submerged electrodes and replenishing the HC1 content by introductionof HC1.

2. In the manufacture of chlorine, the process whlch compriseselectrolyzing a body of aqueous solution. of HC1 between a pair ofsubmerged electrodes and replenishing the HCl content by introduction ofHCl gas at a point below the level of the electrode.

3. In a chlorine cell, a casing, an annular anode therein, a annularcathode, an axial dependlng chamber in open communication with thechamber formed by the cathode and means for introducing HC1 gas near thebottom of the depending chamber.

4. In the manufacture of chlorine, thc process whlch compriseselectrolyzing a bath composed of a solution of I-ICl between submergedelectrodes with introduction of replenishmg gaseous HCL near the bottomof said bath, the height of liquid column above the point ofintroduction being suiicient to effect substantially complete absorptionby the bath of the gaseous HC1 so introduced.

5. In the manufacture of chlorine, the

process which comprises electrolyzing a continuously replenished bath ofHCl solution replenishment being by gaseous HC1. y In testimony whereof,I have hereunto affixed my signature.

FRANK S. LOW.

